This invention relates to multilayer films and, more particularly, to multilayer films which are suitable for the packaging and administration of medical solutions in the form of flexible pouches.
Currently, it is common medical practice to supply medical solutions for parenteral (e.g., intravenous) administration in the form of disposible, flexible pouches. One class of such pouches is commonly referred to as an "I.V. bag." These pouches must meet a number of performance criteria, including collapsibility, optical clarity and transparency, high-temperature heat-resistance, and sufficient mechanical strength to withstand the rigors of the use environment. Medical solution pouches must also provide a sufficient barrier to the passage of moisture vapor and other gasses to prevent contamination of the solution contained therein.
Collapsibility is necessary in order to ensure proper and complete drainage of the pouch. Unlike rigid liquid containers which rely on air displacement for drainage, medical solution pouches rely on collapsibility for drainage. As the pouch drains, atmospheric pressure collapses the pouch at a rate which is proportional to the rate of drainage. In this manner, the pouch can be fully drained and at a substantially constant rate. In order for the pouch to be collapsible, the film from which the pouch is made must be flexible. If the film is too stiff, the pouch cannot drain fully and, as a result, the patient may not receive the intended quantity of medical solution. Thus, a key consideration in the design of films used to produce medical solution pouches is that the film must have sufficient flexibility that the resultant medical pouch is collapsible enough to be fully drainable.
Prior to administering a medical solution from a pouch and into a patient, a visual inspection of the solution contained within the pouch is performed by the medical professional who is performing the administration procedure. Such an inspection provides a cursory determination that the medical solution to be administered is of the proper type and has not deteriorated or become contaminated. In this regard, it is essential that the pouch have excellent optical properties, i.e., a high degree of clarity and transmission and a low degree of haze. A medical solution pouch having poor optical properties can easily render a visual inspection of the packaged solution ineffective, thereby causing the medical professional to needlessly discard the pouch. Worse, the medical professional could fail to notice a solution which is of the wrong type, or which had deteriorated or become contaminated. As will be discussed more fully below, the industry-wide practice of heat-sterilizing solution-containing medical pouches greatly exacerbates the problem of maintaining good optical properties in such pouches.
Heat-sterilization of solution-containing medical pouches typically occurs in an autoclave at about 250.degree. F. for periods of 15 to 30 minutes. Steam is generally used as the heat-transfer medium. Heat-sterilization is normally performed by the manufacturer and/or packager of the medical solution prior to sending the packaged medical solution to the end user, e.g., a hospital. This helps to ensure that the medical solution, as packaged in the medical solution pouch, will be substantially free from contamination. Thus, another requirement of medical solution pouches is that they must be able to endure the high temperatures which are encountered during heat-sterilization without deterioration by, e.g., developing a heat-seal leak or other type of containment failure.
Medical solution pouches must also have sufficient mechanical strength to withstand the abuse which is typically encountered in the use environment. For example, in some circumstances, a plastic or rubber bladder is placed around a medical solution-containing pouch and pressurized to, e.g., 300-400 mm/Hg, in order to force the solution out of the pouch an into a patient. Such a bladder is commonly referred to as a "pressure-cuff" and is used, e.g., when a patient is bleeding profusely in order to quickly replace lost fluids or, e.g., when a patient has high blood pressure such that a greater opposing pressure must be generated in the pouch in order to introduce medical solution into the patient's veins. Medical solution pouches should have sufficient durability to remain leak-free during such procedures.
At present, flexible pouches for medical solution packaging are typically made from a highly plasticized polyvinyl chloride (PVC). While generally meeting the requirements mentioned above, PVC may have some undesirable properties for use as a medical solution pouch. For example, plasticizer can migrate from the PVC pouch and into the solution contained within the pouch so that the solution may become contaminated by potentially toxic material. A question has also arisen concerning whether PVC is adequately chemically neutral to medical solutions. It also been found that PVC becomes brittle at relatively low temperatures.
For these reasons, alternatives to PVC pouches have been sought. Such alternative pouches are typically formed from polyolefin-containing, multilayer films wherein one exterior layer of the film is an abuse-resistant layer and forms the outside of the pouch, while the other exterior layer of the film is a heat-seal layer, i.e., a layer able to seal to itself upon the application of sufficient heat, and forms the inside of the pouch. A core layer is generally provided as an interior layer in the film to impart strength and flexibility to the film, as well as to contribute to the gas impermeability of the film.
A particularly difficult challenge in the design and manufacture of polyolefin-based films which are used to produce medical solution pouches is the ability of the film to provide the above performance criteria after the pouch has been heat-sterilized. That is, the high temperatures and steam which are encountered during heat-sterilization can adversely affect the collapsibility, mechanical strength, and optical properties of the pouch.
Of particular concern is the adverse effect of heat-sterilization on the optical properties of medical solution pouches. In general, the gas permeability of polyolefin-based films is directly proportional to the temperature of such films. Thus, gas permeability increases with increasing temperature and vice versa. During heat-sterilization, the gas permeability of polyolefin-based medical solution pouches is significantly higher than when such pouches are at room temperature. As a result, the steam which is used to heat the pouches penetrates into the film from which the pouch has been formed. When the sterilization process is completed and the pouch is allowed to cool, some of the steam in the film often condenses and remains trapped inside the film, primarily in the core layer since it is generally the thickest layer of the film. The trapped condensate gives the pouch a hazy, cloudy appearance which can make it difficult to inspect the medical solution contained within the pouch as described above. In addition, the hazy appearance is aesthetically unappealing.
Accordingly, a need exists in the art for a multilayer, polyolefin-based film which is a suitable replacement for PVC as a material for the manufacture of medical solution pouches, and which has improved optical properties after the pouch has been heat-sterilized.